The overall goal of the proposed experiments is the elucidation of the sequence organization of endogenous type-C retrovirus genes (RD114 and FeLV) of domestic cat cells, and of exogenously infected mammalian cells, relative to their biological activity. In these cells containing virus-related DNA sequences, infectivity of the cell DNAs by transfection techniques is correlated 100% with virus expression. Most cat cell DNAs, all of which contain approximately 20 copies of integrated RD114 viral-related sequences, are not infective and the cells do not express virus. We predict, on the basis of DNA specific infectivities and preliminary restriction enzyme mapping that only one or a few of the 20 RD114-related provirus sequences in virus-expressing cat cells are virus productive and infectious, whereas a much higher proportion of the exogenous RD114 genes (3-5 copies) in heterologous hosts will be infective. We propose to clone all viral-related endogenous RD114 sequences of the cat cell genomes, as well as those of exogenously infected human and dog cells using DNA recombinant techniques, and to compare the infectivities of the cloned sequences in sensitive cell lines, and their sequence organization by restriction enzyme mapping, Southern blotting and hybridization with appropriate c-DNA probes. FeLV sequences, which are normally not infective, are of interest because of a potential chromosomal linkage with RD114, and will be tested for in RD114 clones. The data obtained, in conjuction with the previously determined restriction maps of unintegrated linear provirus, will allow us to determine the number of infectious proviral DNAs in a given cell line, as well as the sequence organization consistent with infectivity. Further, we hope to deduce the nature of the differences in sequence arrangement between active and inactive viral genes, whether due to small genone deletions, divergence of sequences, host flanking or intervening sequences, or other modifications, and thus shed some light on the factors which control the expression of viral genes in eucaryotic cells.